This invention is directed to additives which improve the low-temperature properties of distillate fuels and to fuel compositions containing minor amounts of same.
Traditionally, the low-temperature properties of distillate fuels have been improved by the addition of kerosene, sometimes in very large amounts (5-70 wt %). The kerosene dilutes the wax in the fuel, i.e. lowers the overall weight fraction of wax, and thereby lowers the cloud point, filterability temperature, and pour point simultaneously. The additives of this invention effectively lower both the cloud point and CFPP of distillate fuel without any appreciable dilution of the wax component of the fuel.
Other additives known in the art have been used in lieu of kerosene to improve the low-temperature properties of distillate fuels. Many such additives are polymeric materials with pendent fatty hydrocarbon groups, and are usually derived from the free radical polymerization of unsaturated hydrocarbons (olefins, acrylates, fumarates, etc.). These additives are limited in their range of activity, however; most improve fuel properties by lowering the pour point and/or filterability temperature. These same additives have little or no effect on the cloud point of the fuel.
The additives of this invention are substantially different, however, both in terms of structure and function. They are oligomeric and/or polymeric materials obtained via condensation reactions, e.g. the reaction of diols with acids and/or anhydrides. In terms of activity, these additives effectively lower distillate fuel cloud point, thus providing improved low-temperature fuel properties, and offering a unique and useful advantage over known distillate fuel additives.
The novel oligomeric/polymeric benzophenone tetracarboxylate esters and ester/amides of this invention have been found to be surprisingly active wax crystal modifier additives for distillate fuels. Distillate fuel compositions containing less than 0.1 wt % of such additives demonstrate significantly improved low-temperature flow properties, with lower cloud point and lower CFPP filterability temperature.